KINETIC-ANALYSIS OF TAURINE INFLUX INTO CEREBRAL CORTICAL SLICES FROMADULT AND DEVELOPING MICE IN DIFFERENT INCUBATION CONDITIONS

The influx of taurine into cerebral cortical slices was studied with 3 -day-old and 3-month-old mice in different ionic environments in incub ation medium. In standard Krebs-Ringer medium the influx comprised two saturable uptake components, high- and low-affinity, and non-saturabl e penetration. In isoosmotic medium potassium stimulation abolished th e high-affinity uptake in both age groups. In hyperosmotic medium the high-affinity uptake disappeared totally in 3-day-old mice and partial ly in 3-month-old mice. The high-affinity uptake was also obliterated in hypoosmotic medium and in the absence of chloride ions in both age groups. The low-affinity uptake was abolished by potassium stimulation in 3-month-olds and strongly inhibited in 3-day-olds. Hypoosmotic and chloride-free media also inhibited the low-affinity uptake at both ag es. Non-saturable influx was greatly diminished in chloride-free media . The taurine uptake systems are thus strongly inhibited in incubation conditions which simultaneously evoke apparent release of taurine fro m cerebral cortical slices. This inhibition contributes to the magnitu de of the estimated release, which in vitro represents overflow of rel eased taurine molecules which escape recapture by the membrane carrier s. In vivo the same mechanism may underlie the delayed and spreading n euromodulatory actions of taurine.